1. Field of the Invention
The present invention relates to a flame retardant aromatic polycarbonate resin composition. More particularly, the present invention is concerned with a flame retardant aromatic polycarbonate resin composition comprising an aromatic polycarbonate (A), branched metal oxide particles (B), each independently being a branched metal oxide aggregate or a branched metal oxide agglomerate, an alkali metal salt (C) of an organic sulfonic acid, and a fluoropolymer (D), wherein components (A), (B), (C) and (D) are present in specific amounts, respectively. In the resin composition of the present invention, the branched metal oxide particles (B) are dispersed in a mixture of components (A), (C) and (D), wherein at least 70% of the branched metal oxide particles (B) have a diameter within the range of from 10 to 200 nm. The flame retardant aromatic polycarbonate resin composition of the present invention is advantageous not only in that it exhibits excellent flame retardancy without using a bromine-containing flame retardant or a phosphorus-containing flame retardant, but also in that it exhibits excellent melt stability without sacrificing the excellent thermal resistance and impact resistance which an aromatic polycarbonate inherently possesses.
2. Prior Art
A flame retardant aromatic polycarbonate has been widely used as molding materials for housings or parts of various devices, such as a monitor for a personal computer, a notebook computer, a copying machine, a fax machine, a printer, a projector, a portable device, an electric or electronic device and a high precision machine.
In recent years, with respect to various products produced by using an aromatic polycarbonate resin composition, there is a tendency that the wall thicknesses of the products are reduced for the purpose of reducing the weight of the products. Further, such products are required to have an improved flame retardancy from the viewpoint of safety in the accident of fire.
A flame retardant aromatic polycarbonate resin composition which contains a conventional flame retardant containing bromine, phosphorus or silicone has the following problem. The above-mentioned conventional flame retardant has unsatisfactory thermal stability. Therefore, when melt-molding of the resin composition containing such a conventional flame retardant is performed at high resin temperatures, the heat decomposition of the resin composition vigorously occurs, thereby spoiling the properties of the resin composition.
Therefore, the melt-molding of a flame retardant polycarbonate resin composition needs to be performed at moderate resin temperatures within the range wherein the decomposition of the flame retardant resin composition does not occur. As a specific method for performing the molding at such moderate resin temperatures, there has been proposed a method in which an aromatic polycarbonate is blended with another resin (e.g., as an alloy of an aromatic polycarbonate with an acrylonitrile/butadiene/styrene copolymer (ABS resin)), to thereby improve the balance between the melt fluidity and flame retardancy of the resin composition. This method has already been put to practical use.
However, the method in which an aromatic polycarbonate is blended with another resin has a problem in that the excellent properties (such as heat resistance and impact resistance) inherently possessed by an aromatic polycarbonate are spoiled.
Further, in recent years, from the viewpoint of the environmental protection, it has been strongly desired to develop a flame retardant aromatic polycarbonate resin composition which does not contain a bromine-containing flame retardant or a phosphorus-containing flame retardant and, therefore, is less harmful to the environment.
As a method for improving the flame retardancy of an aromatic polycarbonate without using a bromine-containing flame retardant or a phosphorus-containing flame retardant, Examined Japanese Patent Application Publication No. Sho 60-38418 (corresponding to U.S. Pat. No. 4,391,935) discloses a resin composition obtained by blending an aromatic polycarbonate with an alkali metal salt or alkaline earth metal salt of an organic acid and a polytetrafluoroethylene.
However, when the aromatic polycarbonate resin composition described in the above-mentioned patent document is used for obtaining a molded article having a small wall thickness (hereinafter, simply referred to as a “thin molded article”), the following problem arises. For obtaining a thin molded article which has satisfactory excellent flame retardancy, it is necessary to increase the amounts of the above-mentioned metal salt and polytetrafluoroethylene in the resin composition. However, the use of large amounts of the above-mentioned metal salt and polytetrafluoroethylene disadvantageously lowers the melt stability of the resin composition.
Unexamined Japanese Patent Application Laid-Open Specification No. 2001-270983 discloses a resin composition obtained by blending an aromatic polycarbonate with an organosiloxane compound, a fluorine-containing compound and an alkali metal salt of an organic acid. However, since the thermal stability of the organosiloxane compound is unsatisfactory, the melt stability of the resin composition is also unsatisfactory.
Unexamined Japanese Patent Application Laid-Open Specification No. 2001-40202 discloses a resin composition obtained by blending an aromatic polycarbonate with a core-shell graft rubber, a fluorine-containing compound and an alkali metal salt of an organic acid. However, since the thermal stability of the core-shell graft rubber is unsatisfactory, the melt stability of the resin composition is also unsatisfactory.
On the other hand, there is proposed a method in which an aromatic polycarbonate is blended with nanometer-size particles of an inorganic compound.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. Sho 53-25660 discloses a method in which fine particles (having an average particle diameter of 100 nm or less) of an inorganic substance are incorporated into a flame retardant synthetic resin composition. However, since a bromine-containing flame retardant or a phosphorus-containing flame retardant is used in the flame retardant synthetic resin composition, not only is the resin composition disadvantageous from the viewpoint of the environmental protection, but also the dripping of flaming particles cannot be satisfactorily prevented when a molded article obtained from the resin composition is on fire.
WO00/34371 discloses a method in which silicon compound particles having an average particle diameter of 1 nm to 20 μm are incorporated into a flame retardant aromatic polycarbonate resin composition. However, in the working examples of this patent document, a phosphorus-containing flame retardant is used. Therefore, not only is the resin composition obtained in this patent document disadvantageous from the viewpoint of the environmental protection, but also the excellent properties (such as heat resistance and impact resistance) inherently possessed by an aromatic polycarbonate are spoiled.
U.S. Pat. No. 5,274,017, WO00/50511 and Unexamined Japanese Patent Application Laid-Open Specification Nos. 2001-152030 and 2002-60610 disclose a resin composition obtained by blending a thermoplastic resin with fine particles of an inorganic compound. However, the resin composition disclosed in each of these patent documents poses a problem in that a thin molded article obtained from the resin composition exhibits unsatisfactory flame retardancy or the melt stability of the resin composition is unsatisfactory.
Thus, the conventional flame retardant aromatic polycarbonate resin composition has a problem in that the melt stability of the resin composition is poor due to the unsatisfactory thermal stability of a flame retardant used or due to the use of a flame retardant in a large amount which is needed for achieving a high flame retardancy, so that the properties of a shaped article produced from the resin composition are spoiled.
Therefore, it has been desired to develop an aromatic polycarbonate resin composition which exhibits an excellent flame retardancy without using a bromine-containing flame retardant or a phosphorus-containing flame retardant, and exhibits an excellent melt stability without sacrificing the excellent heat resistance or impact resistance which an aromatic polycarbonate inherently possesses.